Double noble metal loaded molecular sieve catalyst for catalyzing oxygen to oxidize methane to prepare acetic acid

Abstract

The invention belongs to the field of catalytic materials, and particularly discloses a double noble metal supported molecular sieve catalyst for catalyzing oxygen to oxidize methane to prepare acetic acid. The preparation method comprises the following steps: mixing a chloroauric acid solution and another noble metal chloride solution as precursors with a molecular sieve, adjusting a certain pH value, stirring and aging at a proper water bath temperature for a certain time, and then filtering, drying and calcining to obtain the catalyst. According to the catalyst, a molecular sieve is used as a carrier, gold is used as an oxidation active center, carbon-carbon coupling is achieved with another precious metal, high-selectivity acetic acid preparation through methane pure oxygen direct oxidation can be achieved under the mild condition of 120-240 DEG C, and the selectivity reaches up to 97.2%. The catalyst preparation method adopted by the invention is simple in process, green and pollution-free, high in noble metal loading efficiency, low in price and easy for expanded production, and provides a thought for developing and preparing a high-efficiency catalyst for direct selective oxidation of methane under mild conditions.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic materials, and particularly relates to a dual-noble-metal supported molecular sieve catalyst for catalytic oxidation of methane to acetic acid with oxygen. Background Art

[0002] Methane (CH4) is the simplest alkane in structure and has the highest hydrogen-carbon ratio. As the main component of natural gas, its proportion is about as high as 84%, and it is an abundant and clean fossil energy source. At the same time, it is also the second-largest greenhouse gas emitted globally after carbon dioxide and is a key component contributing to ozone layer depletion. Therefore, the efficient utilization of methane can not only alleviate the crisis of the increasingly depleted fossil resources but also be of great significance for eliminating the greenhouse effect. Therefore, directly and selectively converting methane into high-value-added chemicals is an important approach and scientific challenge for the rational development and utilization of methane resources at present. In recent years, it has become one of the research hotspots attracting much attention from global researchers. However, the methane molecule has a symmetric tetrahedral configuration, and the bond energy of its C-H bond is as high as 439 kJ / mol -1 , and at the same time, its low electron affinity (-1.9 eV), small polarizability (2.84×10 -40 C 2 m 2 J -1 ), making the activation and conversion of methane extremely difficult.

[0003] Acetic acid (CH3COOH) is widely used as a product or raw material in fields such as the food industry, biopharmaceuticals, and the production of high-grade chemical products. Currently, there are mainly two methods for preparing acetic acid: chemical synthesis and biological fermentation. Among them, the output of the biological fermentation method only accounts for 10% of the total acetic acid output and is mainly used in biological preparations and the food industry. Most acetic acid is produced by chemical synthesis methods. The method of producing acetic acid by carbonylation of methanol and carbon monoxide is the most widely used. It is necessary to prepare syngas (CO + H2) by dry reforming (DRM) or steam reforming (SRM) reactions of resources such as methane or coal under high temperature and high pressure conditions. Subsequently, the syngas undergoes a catalytic reaction to generate methanol (CH3OH), and then acetic acid is generated by carbonylation of methanol and carbon monoxide. This process has difficult-to-solve problems such as a long reaction path, high energy consumption, low atom utilization rate, and serious environmental pollution, increasing the economic cost and environmental pressure. Therefore, researchers have developed a series of catalysts to achieve direct selective oxidation of methane to acetic acid. In the early homogeneous catalytic system, the Periana research group catalyzed the conversion of methane to acetic acid by PdSO4 in concentrated sulfuric acid, and the selectivity could reach 72% (R.A. Periana, O. Mironov, D. Taube et al. Science 2003). Later, the Fujiwara research group achieved the efficient generation of acetic acid using the VO(acac)2 catalyst in the presence of CF3COOH and K2S2O8, and its TON could reach 27.5 (Y. Taniguchi, T. Hayashida, H. Shibasaki et al. Org. Lett. 1999). However, the above homogeneous reaction systems not only have difficult catalyst preparation methods and harsh catalytic reaction conditions, but also have problems such as difficulty in separating the catalyst from the product and the corrosiveness of strong acids and oxidants, making it difficult to be applied industrially. The research on selective oxidation of methane to acetic acid under heterogeneous catalytic systems has more advantages in terms of product separation and catalytic activity and has been widely studied in recent years. In 2017, the Shan research group used the synthesized Rh / ZSM-5 catalyst at 150 °C. Under the condition of the simultaneous presence of CO and O2, after reacting for 3 hours, the acetic acid yield could reach 22,000 μmol / g cat, the acetic acid selectivity was 60% (J. Shan, M. Li, L. F. Allard et al. Nature 2017). In 2022, the applicant's team used the Au / ZSM-5 catalyst to achieve the catalytic selective oxidation of methane to acetic acid and methanol with O2 at 120 - 240 °C, and the acetic acid selectivity was 53% (Guodong Qi, Jun Xu, Graham J. Hutchings et al. Nat. Catal. 2022). In 2024, the Zhang Tao research group developed a M1-ZSM-5 (M = Pd, Rh, Ru, Fe) catalyst. Through the strategy of carbon monoxide (CO) molecule modification, under the condition of using hydrogen peroxide (H2O2) as the oxidant, the direct selective oxidation of methane to acetic acid at room temperature was achieved, and the TOF of acetic acid = 207 h -1 , and the acetic acid selectivity was close to 100% (W. Xu, X. Wang, T. Zhang et al. Angew. Chem. Int. Ed. 2024). However, in these heterogeneous catalytic systems, in most cases, the co-participation of CO / H2O2 in the reaction is required to produce acetic acid with high selectivity, resulting in high industrialization costs. In addition, the selectivity of catalytic methane to acetic acid using pure O2 as the oxidant is low. The main reason is that the product acetic acid is more likely to be peroxidized to CO2 under oxygen conditions. The difficulty lies in regulating the oxygen activation ability of the prepared catalyst to obtain higher product selectivity. Therefore, it is of great significance to design and develop a new catalyst with simple preparation, low price, and easy industrial scale-up to achieve the efficient selective oxidation of methane to acetic acid with pure O2 as the oxidant under mild conditions. Summary of the Invention

[0004] To overcome the disadvantages of complex process and environmental pollution in the acetic acid production process in the above-mentioned background technology, the present invention develops a dual-noble-metal-loaded molecular sieve catalyst for catalytic oxidation of methane with oxygen to acetic acid. The catalyst uses a molecular sieve as the carrier, uses gold as the oxidation active center, and another noble metal to achieve carbon-carbon coupling. It can achieve the direct oxidation of methane with pure oxygen to acetic acid with high selectivity under mild conditions of 120 - 240 °C, with a selectivity as high as 97.2%. The other main by-products are methanol, peroxy-methanol, peroxy-acetic acid, etc. The catalyst preparation method adopted in the present invention has a simple process, is green and pollution-free, has a high noble metal loading efficiency, is cheap, and is easy to scale up production, providing an idea for the development and preparation of an efficient catalyst for the direct selective oxidation of methane under mild conditions.

[0005] The present invention adopts the following technical solutions:

[0006] A dual-noble-metal loaded zeolite catalyst for catalytic oxidation of methane to acetic acid with oxygen. The catalyst comprises a zeolite carrier and alloy nanoparticles of dual-noble metals dispersed on the carrier. The dual-noble metals are gold and one selected from another noble metal, palladium, silver, or platinum. The zeolite includes one or more of H-Y zeolite, H-ZSM-5 zeolite, and H-MOR zeolite.

[0007] Preferably, the catalyst comprises a zeolite carrier and Au-Pd alloy nanoparticles dispersed on the carrier.

[0008] Further, the mass percentage of the dual-noble metals on the catalyst is 0.1-1 wt.%, preferably 0.5 wt.%.

[0009] Further, the mass ratio of gold to the other noble metal (palladium, silver, or platinum) in the dual-noble metals is 10:1 to 10:50, preferably 5:1 to 10:30, and most preferably 3:1.

[0010] Further, the SiO2 / Al2O3 molar ratio in the H-Y zeolite is 2 to 10, the SiO2 / Al2O3 molar ratio in the H-ZSM-5 zeolite is 25 to 300, and the SiO2 / Al2O3 molar ratio in the H-MOR zeolite is 10 to 20.

[0011] Further, the D90 particle size of the alloy nanoparticles of the dual-noble metals is 8 to 15 nm.

[0012] Further, the preparation of the catalyst includes: using chloroauric acid solution and another noble metal chloride solution as precursors, mixing with zeolite, adjusting the pH value of the solution to 8 to 10, then aging at a water bath temperature of 40 to 80 °C for 2 to 3 hours. After the solution is cooled to room temperature, it is filtered, washed, dried, and then calcined at 240 ± 5 °C to obtain the dual-noble-metal loaded zeolite catalyst. Among them, ammonia water is used to adjust the pH value of the solution.

[0013] A preparation method of a dual-noble-metal loaded zeolite catalyst for catalytic oxidation of methane to acetic acid with oxygen, comprising the following steps:

[0014] (1) Select commercial zeolite carriers with different framework structures. If it is ammonia-type zeolite, it needs to be deaminated at an appropriate temperature to convert it into hydrogen-type, and hydrogen-type zeolite does not need to be treated;

[0015] (2) Add hydrogen-type zeolite to a beaker containing an appropriate amount of deionized water according to a liquid-solid ratio of 50-200 mL:0.5-3 g, and stir to disperse evenly;

[0016] (3) Mix a certain concentration of chloroauric acid solution and another precious metal chloride solution in a certain proportion and add them to a beaker. Use ammonia water to adjust the pH value of the solution to 8 to 10;

[0017] (4) Age the solution with the adjusted pH value at a water bath temperature of 40 to 80 °C and a stirring speed of 500 - 700 rpm for 2 to 3 hours;

[0018] (5) After waiting for the solution to cool to room temperature, carry out filtration separation, washing with deionized water, drying, and then calcine at 240 ± 5 °C for 0.5 to 2 hours to obtain a dual-precious-metal loaded molecular sieve catalyst.

[0019] Further, in step (1), the temperature of the deamination treatment is 500 to 650 °C, and the time is 1 to 8 hours.

[0020] Further, in step (3), the concentration of the chloroauric acid solution is 5 - 10 mmol / L, the concentration of the other precious metal chloride solution is 5 - 10 mmol / L, and the concentration of the ammonia water is 0.5 wt% - 5 wt%.

[0021] Further, in step (5), the drying temperature is 60 - 80 °C, and the drying time is 12 to 24 hours.

[0022] The application of the above dual-precious-metal loaded molecular sieve catalyst or the dual-precious-metal loaded molecular sieve catalyst prepared by the above method in the catalytic oxidation of methane to acetic acid, preferably in the catalytic oxidation of methane to acetic acid using pure oxygen as the oxidant.

[0023] Further, the application includes: adding the above dual-precious-metal loaded molecular sieve catalyst and an appropriate amount of deionized water to a high-pressure reactor, sealing the reactor, introducing an inert gas into the reactor to displace the air in the reactor, then introducing a certain proportion of CH4 and O2, controlling the reaction pressure to be 10 to 40 atmospheres, heating the reactor to a certain temperature, and reacting for a certain time to obtain acetic acid products.

[0024] Further, the reaction temperature is 120 to 240 °C, and the reaction time is 5 to 960 minutes.

[0025] Further, the ratio of the dual-precious-metal loaded molecular sieve catalyst to deionized water is 10 - 200 mg:5 - 15 mL.

[0026] The advantages and beneficial effects of the present invention are:

[0027] (1) The present invention uses commercial molecular sieve as a carrier, with gold as the oxidation active center and another noble metal (palladium, silver, platinum) to achieve carbon-carbon coupling. It can directly oxidize methane with pure O2 as the oxidant under mild conditions of 120 to 240 °C to produce acetic acid with high selectivity, with a selectivity as high as 97.2%. Moreover, it can maintain a relatively high acetic acid selectivity under long-term reaction conditions, and the other main by-products are methanol, methyl hydroperoxide, peracetic acid, etc.

[0028] (2) The raw materials selected in the present invention are metal chlorides, ammonia water, and commercial molecular sieve. The raw materials are easily available, the process is simple, green, pollution-free, and the operation is simple.

[0029] (3) The prepared double noble metal components of the present invention have high loading efficiency, and the content can be adjusted, enabling the regulation of acetic acid selectivity in the direct oxidation reaction of methane.

[0030] (4) The molecular sieve carrier of the present invention has highly dispersed alloy nanoparticles of gold and another noble metal. Among them, the Au-Pd alloy nanoparticles with a particle size concentrated in the range of 8 to 15 nm have the best catalytic activity.

[0031] (5) The catalyst of the present invention can be reused and has high stability. The reason is that the molecular sieve carrier has good hydrothermal stability and a large number of acid centers that can serve as binding sites for alloy nanoparticles, thus improving the stability of the catalyst. Description of the Drawings

[0032] Figure 1 It is the X-ray diffraction spectrum (XRD) of the catalyst sample synthesized in Example 2.

[0033] Figure 2 It is the transmission electron microscopy image (TEM) of the catalyst sample synthesized in Example 8.

[0034] Figure 3 It is the transmission electron microscopy image (TEM) of the catalyst sample synthesized in Example 11.

[0035] Figure 4 It is the liquid nuclear magnetic resonance spectrum of the liquid product after the catalytic methane oxidation reaction of the catalyst sample synthesized in Example 3. Detailed Embodiments

[0036] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the solution of the present invention is now provided. However, it should not be construed as a limitation on the scope of implementation of the present invention. The following provides a detailed description of the present invention through specific examples.

[0037] Preparation of the Catalysts in Examples 1 - 13

[0038] The preparation of the catalysts of Examples 1-13 includes carrier pretreatment and loading of the double noble metal active components onto the carrier. The carrier is a commercial ZSM-5, H-Y, and MOR molecular sieve carrier, and the double noble metal active site is an Au and Pd alloy. The theoretical mass fractions of Au and Pd are 0.375% and 0.125% respectively.

[0039] The preparation method of the catalysts of Examples 1-13 includes the following steps:

[0040] Step 1 Select commercial ZSM-5 or MOR molecular sieves with different silica-alumina ratios as the carrier, and treat it at 550 °C for 6 hours to perform deamination to convert it into a hydrogen-type molecular sieve.

[0041] Step 2 Add 1 g of the hydrogen-type molecular sieve carrier to a beaker containing 67 mL of deionized water, and stir for 30 minutes at a rotation speed of 600 revolutions per minute.

[0042] Step 3 Mix 3.18 mL of a 6 mmol / L HAuCl4 aqueous solution and 1.97 mL of a 6 mmol / L PdCl2 aqueous solution, then add them to the beaker. Adjust the pH value of the solution to a certain fixed value within 6 to 12 using 2.5 wt% ammonia water, and maintain it for 30 min.

[0043] Step 4 Stir and age the resulting solution at a water bath temperature of 40 to 80 °C at a rotation speed of 600 revolutions per minute for 1 to 3 hours.

[0044] Step 5 After waiting for the solution to cool to room temperature, perform filtration separation, wash with deionized water to obtain a solid sample, and then dry it at 60 °C for 24 hours.

[0045] Step 6 Heat-treat the obtained dried sample at 240 °C for 1.5 hours under air conditions to obtain the catalyst.

[0046] Preparation of the catalyst of Comparative Example 1

[0047] According to the catalyst preparation method of the above Examples 1-13, replace the Au-Pd bimetal with an Au-Mo bimetal, where the theoretical mass fractions of Au and Mo are 0.375% and 0.125% respectively.

[0048] Step 1 Select ZSM-5 (SiO2 / Al2O3 = 25) molecular sieve as the carrier, and treat it at 550 °C for 6 hours to perform deamination to convert it into a hydrogen-type molecular sieve.

[0049] Step 2 Add 1 g of the hydrogen-type molecular sieve carrier to a beaker containing 67 mL of deionized water, and stir for 30 minutes at a rotation speed of 600 revolutions per minute.

[0050] In Step 3, 2.16 mL of a 6 mmol / L aqueous solution of (NH4)2MoO3 and 3.18 mL of a 6 mmol / L aqueous solution of HAuCl4 were mixed and added to a beaker. The pH value of the solution was adjusted to 10 with 2.5 wt% ammonia water and maintained for 30 min.

[0051] In Step 4, the resulting solution was stirred and aged at 60 °C in a water bath at a rotation speed of 600 rpm for 2 hours.

[0052] In Step 5, after waiting for the solution to cool to room temperature, it was filtered and separated, washed with deionized water to obtain a solid sample, and then dried at 60 °C for 24 hours.

[0053] In Step 6, the obtained dried sample was heat-treated at 240 °C in air for 1.5 hours to obtain the Au-Mo / ZSM-5 catalyst.

[0054] As shown in Table 1, the inductively coupled plasma was used to test and analyze the actual metal loading of the catalysts prepared in the above examples. It can be seen from Examples 2-5 that as the SiO2 / Al2O3 molecular ratio on the ZSM-5 support increases, the actual metal loading will slowly decrease, but the actual metal loading rate is higher than 90%, indicating that zeolites with a low SiO2 / Al2O3 ratio are more conducive to the loading of the bimetal; comparing Example 2 and 6 in Table 1, it can be seen that although the MOR zeolite has a lower SiO2 / Al2O3 ratio than ZSM-5, its metal loading efficiency is much lower than that of the ZSM-5 zeolite support, indicating that different types of zeolite supports also have a significant impact on the actual metal loading; comparing Examples 2, 7, 8 and 9 in Table 1, it can be seen that the pH value in the range of 8 to 12 during the catalyst preparation process has little effect on the metal loading, and the actual metal loading rate is close to 100%; comparing Examples 2, 10 and 11 in Table 1, it can be seen that the metal loading gradually decreases with the extension of the aging time; comparing Examples 1, 2 and 12 in Table 1, it can be seen that the metal loading decreases significantly with the increase of the aging temperature. It can be seen from Comparative Example 1 in Table 1 that when the loaded metal is adjusted to Au-Mo, the catalyst obtained by the preparation method of the present invention can achieve an actual metal loading on the catalyst close to the theoretical feed amount. By analyzing the actual metal loading of different examples in Table 1, using a ZSM-5 zeolite support with a SiO2 / Al2O3 ratio of 25, a pH of 10, and aging at 60 °C for 2 hours and other conditions, an actual metal loading on the catalyst close to the theoretical feed amount can be achieved, indicating that the preparation method of the present invention has high efficiency in noble metal loading.

[0055] Table 1. Inductively coupled plasma test (ICP) results of metal loading of samples in different examples

[0056]

[0057] Note: "SiO2 / Al2O3" in Table 1 refers to the molar ratio of silicon dioxide to aluminum oxide in the molecular sieve.

[0058] Characterization of the catalyst

[0059] The sample synthesized in Example 2 was tested by X-ray diffraction spectrum (XRD). The test results are as Figure 1 shown. The results show that the sample has an obvious MFI structure and no obvious diffraction peaks of metallic Au and Pd, indicating that the double noble metals form an alloy and are uniformly dispersed on ZSM-5.

[0060] The sample synthesized in Example 8 was tested by transmission electron microscopy (TEM). The test results are as Figure 2 shown. The results show that the noble metal particles are uniformly dispersed on the ZSM-5 support.

[0061] The sample synthesized in Example 11 was tested by transmission electron microscopy (TEM). The test results are as Figure 3 shown. The results show that the noble metal particles are uniformly dispersed on the ZSM-5 support.

[0062] Performance test of the catalyst for methane oxidation reaction

[0063] The catalysts prepared in Examples 1–13 and Comparative Example 1 were used for the catalytic oxidation of methane to prepare acetic acid. The specific steps are as follows:

[0064] Step 1: Use a 25 mL high-pressure reactor as the reaction vessel. Take 100 mg of the catalyst prepared in Examples 1-13 and 15 mL of deionized water and add them to the reactor.

[0065] Step 2: Seal the reactor, continuously introduce N2 at 1 atmospheric pressure into the reactor and purge for 30 minutes, then introduce CH4 at 10 atmospheric pressures and purge 3 times, and finally introduce CH4 at 20.7 atmospheric pressures and O2 at 3.5 atmospheric pressures as the reaction gas.

[0066] Step 3: Heat the high-pressure reactor to 240 °C and react at this temperature for 60 minutes. Stop heating and cool the high-pressure reactor to below 10 °C using an ice-water bath.

[0067] Step 4: Collect the post-reaction gas and detect the gas-phase products by gas chromatography, and collect the post-reaction liquid and detect the liquid-phase products by liquid nuclear magnetic resonance spectrometer (D2O as the lock-field solvent). As Figure 4 shown, it is the nuclear magnetic resonance analysis spectrum of the liquid product after the reaction of the catalyst synthesized in Example 3 for the catalytic oxidation of methane to prepare acetic acid. It can be seen that the main liquid product is acetic acid, and a small amount of methanol also exists.

[0068] The catalysts prepared in the above examples were used for the reaction of catalytic methane oxidation to produce acetic acid (the corresponding results are shown in Table 2). It can be seen from Examples 2-5 in Table 2 that as the silica-alumina ratio of the support ZSM-5 increases, the yield of liquid oxygenates generally shows a gradually decreasing trend. Among them, the catalyst prepared in Example 2 has the highest yield of liquid oxygenates, and the catalyst prepared in Example 4 has the highest acetic acid selectivity. Comparing Examples 2, 6, and 13 in Table 2, it can be seen that different molecular sieve supports have a significant impact on the yield of liquid oxygenates and acetic acid selectivity. The acetic acid selectivities of the catalysts prepared with H-ZSM-5, H-MOR, and H-Y molecular sieves as supports are all higher than 85%. Comparing Examples 2, 7, 8, and 9 in Table 2, it can be seen that as the pH value increases during the catalyst preparation process, the yield of liquid oxygenates and acetic acid selectivity show a trend of first increasing and then sharply decreasing. When the pH value is 10, the catalyst obtains the highest yield of oxygenates and acetic acid selectivity. When the pH is 6, it is not conducive to the loading of Pd metal, and it is difficult to form an alloy subsequently. And when the pH is 12, the strong alkaline condition will damage the properties of the ZSM-5 support, thereby reducing the activity. Therefore, a pH of 8 to 10 is recommended. Comparing Examples 2, 10, and 11 in Table 2, it can be seen that as the aging time prolongs, the yield of liquid oxygenates and acetic acid selectivity show a trend of first increasing and then decreasing. When the aging time is 2 hours, the catalyst obtains the highest yield of oxygenates and acetic acid selectivity. When the aging time is 1 hour, it is not conducive to the deposition and loading of the bimetal on the support to form an alloy state. When the aging time exceeds 3 hours, the bimetal will be significantly lost. Therefore, an aging time of 2 to 3 hours is recommended. Comparing Examples 1, 2, and 12 in Table 2, it can be seen that as the aging temperature increases, the yield of liquid oxygenates shows a trend of first increasing and then decreasing, and the acetic acid selectivity gradually decreases, but is all higher than 85%. Therefore, an aging temperature of 40 to 80 °C is recommended. Analyzing the liquid-phase products after the reaction of catalytic methane oxidation to produce acetic acid with the catalysts of different examples in Table 2, it can be seen that the catalysts prepared under different conditions can all catalyze the oxidation of methane to produce acetic acid under this reaction condition, and the highest acetic acid selectivity is 97.2%. Example 14 in Table 2 is the experimental data of methane oxidation after the catalyst of Example 11 is reused and recovered 3 times. The specific operation is to filter the catalyst after the reaction of Example 11, wash it with deionized water, and dry it at 60 °C for 12 h. Then, the obtained dried sample is heat-treated at 240 °C for 1.5 h in an air atmosphere to obtain the post-reaction catalyst and then conduct the methane oxidation reaction again. Repeat the above operation 3 times to obtain the final data of Example 14. It can be seen that although the catalyst activity decreases, the acetic acid selectivity can still reach 86.6%, proving that the catalyst obtained in the present invention maintains good acetic acid selectivity during repeated use. Example 15 in the table is the data of Example 2 catalyst reacting for 16 h under the same reaction conditions. Comparing Examples 2 and 15, it can be seen that the catalyst prepared in the present invention maintains a relatively high acetic acid selectivity after a long-time reaction.It can be seen from the comparison between Example 2 and Comparative Example 1 in the comparison table that the acetic acid selectivity after the methane oxidation reaction using the Au-Mo / ZSM-5 catalyst prepared by the preparation method of the present invention is significantly lower than that of the Au-Pd / ZSM-5 catalyst, proving that the dual noble metal components in the present invention have an obvious promoting effect on improving the acetic acid selectivity in the methane oxidation reaction.

[0069] Table 2. Evaluation results of the catalytic reaction performance of the samples in each example

[0070]

[0071]

Claims

1. A dual-noble-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid with oxygen, characterized in that, The catalyst includes a molecular sieve support and alloy nanoparticles of double noble metals dispersed on the support. The double noble metals are gold and one selected from another noble metal, palladium, silver, and platinum. The molecular sieve includes one or several of H-Y molecular sieve, H-ZSM-5 molecular sieve, and H-MOR molecular sieve.

2. The dual-precious-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid according to claim 1, characterized in that, The mass ratio of gold to the other noble metal in the double noble metals is 10:1 to 10:50, preferably 5:1 to 10:30, and most preferably 3:

1. The mass percentage of the double noble metals on the catalyst is 0.1-1 wt.%, preferably 0.5 wt.%.

3. The dual-noble-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid according to claim 1, characterized in that, The SiO2 / Al2O3 molecular ratio in the H-Y molecular sieve is 2 to 10, the SiO2 / Al2O3 molecular ratio in the H-ZSM-5 molecular sieve is 25 to 300, and the SiO2 / Al2O3 molecular ratio in the H-MOR molecular sieve is 10 to 20.

4. The dual-noble-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid according to claim 1, wherein, The D90 particle size of the alloy nanoparticles of the double noble metals is 8 to 15 nm.

5. The dual-precious-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid according to claim 1, characterized in that Preparing the catalyst includes: using chloroauric acid solution and another noble metal chloride solution as precursors, mixing with the molecular sieve, adjusting the pH value of the solution to 8 to 10, then aging at a water bath temperature of 40 to 80 °C for 2 to 3 hours. After the solution is cooled to room temperature, it is filtered, washed, dried, and then calcined at 240±5 °C to obtain the double noble metal supported molecular sieve catalyst.

6. The preparation method of the dual-noble-metal-loaded molecular sieve catalyst for catalytic oxidation of methane to acetic acid according to any one of claims 1-5, characterized in that, It includes the following steps: (1) Select commercial molecular sieve supports with different framework structures. If it is an ammonia-type molecular sieve, it needs to be deaminated at an appropriate temperature to be converted into a hydrogen type, and the hydrogen-type molecular sieve does not need to be treated. (2) Add the hydrogen-type molecular sieve to a beaker containing an appropriate amount of deionized water according to a liquid-solid ratio of 50-200 mL:0.5-3 g, and stir to disperse evenly. (3) Mix a certain concentration of chloroauric acid solution and another noble metal chloride solution in a certain proportion and then add them to the beaker, and use ammonia water to adjust the pH value of the solution to 8 to 10. (4) Age the solution with the adjusted pH value at a water bath temperature of 40 to 80 °C and a stirring speed of 500-700 rpm for 2 to 3 hours. (5) After waiting for the solution to cool to room temperature, carry out filtration separation, washing with deionized water, drying, and then calcine at 240±5 °C for 0.5 to 2 hours to obtain the double noble metal supported molecular sieve catalyst.

7. The preparation method according to claim 6, wherein In step (1), the temperature of the deamination treatment is 500 to 650 °C, and the time is 1 to 8 hours. In step (3), the concentration of the chloroauric acid solution is 5-10 mmol / L, the concentration of the other noble metal chloride solution is 5-10 mmol / L, and the concentration of the ammonia water is 0.5 wt%-5 wt%. In step (5), the drying temperature is 60-80 °C, and the drying time is 12 to 24 hours.

8. Application of the double noble metal supported molecular sieve catalyst according to any one of claims 1-5 or the double noble metal supported molecular sieve catalyst prepared by the method according to any one of claims 6-7 in the catalytic oxidation of methane to acetic acid, preferably in the catalytic oxidation of methane to acetic acid using pure oxygen as the oxidant.

9. The application according to claim 8, characterized in that, The application includes: adding the double noble metal-loaded molecular sieve catalyst and an appropriate amount of deionized water into a high-pressure reactor, sealing the reactor, introducing an inert gas into the reactor to displace the air in the reactor, then introducing a certain proportion of CH4 and O2, controlling the reaction pressure to be 10 to 40 atmospheres, heating the reactor to a certain temperature, reacting for a certain period of time, and obtaining an acetic acid product.

10. The application according to claim 9, wherein The reaction temperature is 120 to 240 °C, and the reaction time is 5 to 960 minutes; The ratio of the double noble metal-loaded molecular sieve catalyst to deionized water is 10 - 200 mg: 5 - 15 mL.

Images